Research has been carried out into the use of recordings of, simulations of and synthesis of intra-uterine sounds for calming babies and has led to the marketing of cassettes containing such recorded sounds and of synthesizers for generating such sounds.
This form of sound has however generally only been found to be effective with babies of up to six weeks of age.
The existing intra-uterine sound methods using cassettes are cumbersome as they involve a cassette player, heavy usage of batteries, and are dangerous to run on mains close to the baby or obtrusive to the environment is located far away from the baby and set at an appropriate sound level. Furthermore, the cassettes are relatively expensive and the synthesizer even more so.